1. Field of the Invention
The invention relates to a method of applying protective layers to components made of oxide dispersion hardened superalloys.
2. Description of the Prior Art
A method of applying protective layers is used in the manufacture of components which are produced from oxide dispersion hardened superalloys. Rotor blades and guide blades and heat-localization segments are examples of components produced from these alloys.
The manufacture of components from an oxide dispersion superalloy begins with the production of the powder which forms the alloy. The metals or metal compounds which are required for manufacturing the powder are mechanically alloyed in a high-energy pulverizer. Basic bodies are first produced from the powder obtained in this way by extrusion. The basic bodies are further processed into the finished components by forging, rolling, and/or machining. The oxide dispersion hardened superalloys used in manufacture contain chromium, aluminum, titanium, molybdenum, tungsten, tantalum, zirconium, boron, nickel and yttrium oxide as essential components.
Gas turbine components are subjected to the effects of high temperatures of more than 600.degree. C. and corrosion due to contact with corrosive substances at high temperatures. For this reason they have to be provided with a protective layer which protects the components from sulfur, oil, acids, oxygen, alkaline earths, and vanadium to slow down the corrosive effects of these substances.
It is known to protect components of this type made of oxide dispersion hardened superalloys from the effect of corrosive substances by applying MCrAlY (M=metal), NiCrAlY, or CoCrAlY protective layers. If the components are, however, subjected to the effects of high temperatures, as is the case under working conditions, diffusion processes occur. Pores form as a result of the diffusion processes, in particular in the boundary region between the component and the applied protective layer as a result of the enrichment and agglomeration of the yttrium oxide particles which are distributed on the surface of the component. Disadvantageous enrichment and agglomeration of the yttria particles can also occur during coating. The quality of the coating and the adhesive properties of the protective layers are thus severely impaired and the life of the materials to be protected is reduced, with the protective layers chipping off after a short time as a result of pore formation.